1. Field of the Invention
This invention relates to impact printers. More specifically, it relates to the cardholder mechanism in such impact printers.
2. Description of the Prior Art
Impact printers have traditionally used cardholders or sheet holders to maintain sheet of printing media flush against the platen of the printer. Conventionally, such cardholders have an inner surface with a curvature essentially corresponding to the curvature of the platen and are mounted adjacent to but spaced from the platen so that a sheet of printing medium may be inserted between the cardholder and the platen. The cardholder, of course, has an opening therethrough so that the impact means may be selectively activated through the opening to print upon the sheet. Conventionally such impact printing is carried out by moving the printer ribbon along a path between the cardholder and the printer disk or daisy wheel containing the characters to be printed on a plurality of radial petals. When a selected character is to be printed, the wheel is rotated into the particular print position after which impact means such as the hammer or missile drive the selected petal against the ribbon to drive the ribbon through the opening in the cardholder to impact the selected character upon the sheet of paper or other printing medium.
In an attempt to meet the ever-increasing demand in the printer field for higher and higher printing speed in excess of 50 characters per second and approaching 100 characters per second, designers of impact printers have been attempting to minimize the flight path of the selected character petal, i.e., the distance that the petal must travel in driving the ribbon against the sheet. In this connection, distances in the order of 1/10th of an inch between the face of the printer wheel petal and the platen would not be unreasonable in high speed printers. Since the ribbon, the cardholder and the paper all must fit and be translationally movable within this limited space, problems of maintaining very close tolerances between these elements are presented. Such problems involve maintaining the necessary spatial relationship between the sheet, the cardholder and the ribbon in initially setting up the printer as well as when it becomes necessary to move the cardholder for cleaning or other maintenance problems when the equipment is on-line. When the cardholder is periodically adjusted, it must be mounted in such a position that its distance from the platen is sufficient to accommodate the sheet of printing media. Similarly, the ribbon must be adjusted with respect to the cardholder in the appropriate spatial relationship so that friction smearing between the two members is minimized. Similarly, translational adjustments of the cardholder in the X and Y direction may require adjustments of the ribbon path in these directions with similar close tolerances as well as corresponding adjustments for a particular end of ribbon sensing means associated with the ribbon.
At best, in conventional printer equipment, the correlation of adjustment of the cardholder, ribbon guide means and end of ribbon sensing means are tedious, time consuming, and require considerable skill.